It is known to conduct enhanced oil recovery (EOR) of hydrocarbons from subterranean hydrocarbon formations after primary recovery processes are no longer feasible. EOR include thermal methods such as in-situ combustion, steam flood, and miscible flooding which use various arrangements of stimulation or injection wells and production wells. In some techniques the stimulation and production wells may serve both duties. Other techniques include steam flooding, cyclic steam stimulation (CSS), in-situ combustion and steam assisted gravity drainage (SAGD). SAGD uses closely coupled, a horizontally-extending steam injection well forming a steam chamber for mobilizing heavy oil for recovery at a substantially parallel and horizontally-extending production well.
Thermal methods of EOR can only be implemented in wells that have been completed for thermal completions. Due to the high temperatures used in thermal completions, wells employing such EOR techniques must be completed using materials, such as steel and cement, that can withstand high temperatures. Wells that were not completed with such high temperature resistant materials cannot implement thermal completions for EOR. Accordingly, well operators must decide on whether or not to implement of thermal EOR and based on this decision complete a well using (or not) high temperature resistant materials.
U.S. Pat. No. 3,196,945 to Forrest et al (assigned to Pan American Petroleum Company) discloses a downhole process comprising a first igniting a reservoir and then injecting air or an equivalent oxygen containing gas in an amount sufficient to create a definite combustion zone or front, the front being at high temperature, typically 800-2400° F. Called forward combustion, Forrest contemplates an oxygen rich front for continued combustion. Demands for large air flow is reduced by co-injection of water or other suitable condensable fluid into the heated formation to create steam front that urges the movement of hydrocarbons or oil. Forrest can co-discharge water and air to the heated formation for creating high temperature steam.
U.S. Pat. No. 4,442,898 to Wyatt (assigned to Trans-Texas Energy Inc.) discloses a downhole vapor generator or burner. High pressure water in an annular sleeve around the burner combustion chamber within which an oxidant and fuel are combusted. The energy from the combustion vaporizes the water surrounding the combustion chamber, cooling the burner and also creating high temperature steam for injection into the formation.
U.S. Pat. No. 4,377,205 to Retallick discloses a catalytic low pressure combustor for generating steam downhole. The steam produced from the metal catalytic supports is conducted to steam generating tubes, and the steam is injected into the formation. Any combustion gases produced are vented to the surface.
U.S. Pat. No. 4,336,839 to Wagner et al (assigned to Rockwell International corp.) discloses a direct firing downhole steam generator comprising an injector assembly axially connected with a combustion chamber. The combustion products, including CO2, are passed through a heat exchanger where they mix with pre-heated water and are ejected out of the generator into the formation through a nozzle.
U.S. Pat. No. 4,648,835 to Eisenhawer et al. (assigned to Enhanced Energy Systems) discloses a direct fire steam generator comprising a downhole burner employing a unique ignition technique using the gaseous injection of a pyrophoric compound such as triethylborane. Natural gas is burned and water is introduced to control combustion. The combustion products, like in Wagner are mixed with water and the resulting steam and other remaining combustion products are injected into the formation.
US Patent Application Publication 2007/0193748 to Ware et al (assigned to World Energy Systems, Inc.) discloses a downhole burner for producing hydrocarbons from a heavy-oil formation. Hydrogen, oxygen and steam are pumped by separate conduits to the burner. A portion of the hydrogen is combusted and the burner forces the combustion products out into the formation. Incomplete combustion is useful in suppressing the formation of coke. The injected steam cools the burner, thereby creating a super heated steam which is also injected into the formation along with the combustion products. CO2 from the surface is also pumped downhole for heating and injection into the formation to solubilise in oil for reducing its viscosity.
In-situ processes to date have not successfully provided economic solutions and have not resolved issues of temperature management, corrosion, coking and overhead associated with existing surface equipment.